Seals lend scientists a helping flipper in the Southern Ocean

They carry ocean sensors to sites where oceanographers struggle to get data.

The standard issue tool for the oceanographer at sea is the Conductivity, Temperature, and Depth instrument (or CTD). These sensors are repeatedly lowered into the water to record vertical profiles of—you guessed it—temperature and electrical conductivity (to measure salinity). This work is expensive, requiring a properly outfitted ship and crew.

But what if you could get a decidedly low-tech piece of equipment to do most of the work for you? Researchers in the Southern Ocean near Antarctica (and elsewhere) have developed a sealCTD—a (small) CTD instrument strapped to a seal, which then gathers data that is otherwise quite hard to come by.

It might seem like the Argo array—an armada of automated floats that carry CTDs throughout the ocean—has already been set up to gather this data. But sea ice and the current that circles Antarctica keep the floats at a distance. Seals, on the other hand, make their living navigating the sea ice in the region.

The project actually started with biologists who wanted to learn more about seal behavior. Oceanographers saw an opportunity in the data and swooped in to continue the work. A recent paper describes a dataset compiled by human scientists, but collected by 349 poorly paid seal assistants (workers that some grad students may identify with), spanning 2004 to 2010.

The average seal dive profiled by the CTDs went to a depth of 500 meters, with some reaching 2,000 meters. The fist-sized instruments, which are glued to a seal’s head and transmit data when it surfaces from a dive, last for about five months before running out of power. Seals molt each year, shedding the instruments along with their fur.

In order to make this cache of data useful, the researchers put the profiles through extensive quality control and calibration. What comes out the other end is just about as good as the Argo data. To see what this gets us, the researchers used a model that takes in available observations and simulates the global ocean circulation pattern that fits them best. This was done for an 18-month period using only the Argo data, and then again using the seal data as well. The two were then compared to see the difference made by the seal data—showing what we would otherwise miss, in other words.

Including the seal data tended to decrease the temperatures estimated for surface water near Antarctica and increase those farther from shore. Salinity increased markedly to the west of the Antarctic Peninsula and lowered a bit elsewhere.

Some of the most interesting differences relate to sea ice behavior. When seawater freezes, salt is excluded from the crystallizing ice. That makes the remaining seawater saltier and, therefore, more dense. The data collected by the seals showed this being more pronounced, affecting surface water circulation. The sea ice itself was also better estimated by the seal-assisted model, with the output comparing more favorably with satellite observations.

“Hey, since you’re going there anyway…” is a phrase usually followed by the words “could you” and a request for some favor. For scientists trying to get data from hard-to-access locations and environments, getting instruments to hitchhike with animals that are going there anyway is obviously an attractive proposition. The Southern Ocean program is growing, and researchers see a lot of untapped potential. Hopefully, the seals don’t mind their high-tech hats.